This invention relates to integrated circuit (IC) film processes and fabrication, and more particularly, to a system and method of inducing, or modifying stress in a deposited film.
After deposition, a first IC film may be subjected to an annealing processes which heats the IC substrate to temperatures of over four hundred degrees C. Often, these annealing processes are done to cure or process subsequently deposited IC films. High temperature annealing processes may unintentional degrade the earlier deposited first IC film.
Some IC films are deposited with an inherent stress. For example, a film may develop a tensile stress after deposition. Alternately, the deposited film may develop a compressive stress. Many films with an inherent tensile stress have poor thermal stability. That is, these tensile stress films have a change of thickness after heating. The tensile stress film has a greater thickness before annealing than after annealing.
A compressive stress film may have a completely different problem. A compressive stress film is likely to buckle upon heating. Buckling or thinning IC films provided unstable mechanical foundation in IC and can seriously interfere with electrical functions. The mismatches between film layers when either type of stress develops can lead to adhesion problems between layers.
To avoid such problems, many IC processes are tempered to minimize the use of high temperatures. Limiting the temperature range of these IC processes imposes serious fabrication restraints, and also affects the quality, operating speed, and usefulness of the resultant IC.
It would be advantageous if a way could be found to use films that develop an inherent stress without degrading the IC product.
It would be advantageous if the inherent stresses of a deposited film could be modified.
It would be advantageous if a film having inherent stress could be loaded on the IC in such away so as to make it thermally stable, or resistant to buckling when heated.
It would be advantageous if the stress between film layers lo could be reduced to promote better layer adhesion.
Accordingly, a method has been provided for forming a stress-loaded first film over a second film. Alternately stated, the method is used to modify the inherent stress in a film to promote a stress-free interface between film layers. The method comprises the steps of:
a) applying a first stress to the top surface of the second film; PA1 b) deposited a first film over the second film, and so translating the first stress applied in Step a) to the first film; PA1 c) releasing the second film from the stress applied in Step a); and PA1 d) in response to releasing the second film from the first stress, loading the first film with a second stress, opposite from the first stress. In this manner, the second film stress is used to load a stress on the first film.
In some aspects of the invention, Step a) includes forming a curve, defined by a first radius, along the second film bottom surface. As a result, a second curve, defined by a second radius, is formed along the first film surfaces. Typically, the bottom surface of the second film is attached to a wafer chuck having a curved mounting surface, whose curve is also defined by the first radius. The stress is provided by securing the second film to wafer chuck.
Step a) includes the first and second radii being in the range between 1 and 1000 meters (m). In one aspect of the invention, the chuck mounting surface is convex so that the first stress on the second film is tensile. Then, Step d) includes the second stress on the first film being compressive. In another aspect of the invention, the chuck mounting surface is concave so that the first stress on the second film is compressive. Then, Step d) includes the second stress on the first film being tensile.
Further steps follow Step d). Step e) anneals the first and second films, and Step f) stops the annealing process after a first time duration. When the first film is loaded with a compressive stress, the first film has a small difference in first thickness, as compared to the originally deposited thickness, after annealing. When the first film is amorphous fluorinated carbon, the difference in thickness is in the range between 0 and 5 percent. The first temperature is in the range between 250 and 450 degrees C. The first time duration is in the range between 15 and 60 minutes.
In some aspects of the invention Step a) includes the first stress on the second film being compressive, and Step d) includes the second stress on the first film being tensile. Then, the first and second films are annealed to form a first film where no buckling has occurred.
A stress-loaded wafer is also provided. The stress-loaded wafer comprises a second film and a first film overlying the second film top surface. The first film has a second stress formed by applying a first, opposite stress to the second film during the deposition of the first film. A second stress loads the first film when the second film is released from the first stress. In this manner, a stress on the second film is used to stress the first film.
As in the above-described method, the first stress is created by forming a first radius curve along the bottom surface of the second film. Likewise, a second radius curve is formed along the first film surfaces. Curves are formed by securing the second film bottom surface to a wafer chuck having a curved mounting surface with a first radius. In this manner, the stresses are provided by securing the second film to the wafer chuck.
The first radius is in the range between 1 and 1000 meters (m). When the first film is amorphous fluorinated carbon, a tensile stress is applied to be second film during the deposition of amorphous fluorinated carbon film. The amorphous fluorinated carbon film is loaded with a compressive stress when the tensile stress is released from the second film. After annealing, the difference in the thickness of the amorphous fluorinated carbon film is less than five percent from the original thickness of the film at deposition.